Resistance device



Aug. 21, 1934. s. RUBEN 1,971,053

RESISTANCE DEVICE Filed Jan. 12, 1935 INVENTOR- JAMUEL RUBEN ATTORNEY-Patented Aug. 21, 1934 RESISTANCE DEVICE Samuel Ruben, New Rochelle, N.Y. Application January 12, 1933, Serial No. 651,278

9 Claims.

ticularly in respect to the material used and to the manufacturethereof. In my co-pending application the resistance base is composed ofa sintered mass of crystals of cuprous oxide having a surface layer ofspecified compounds. I have found that if a compound of cadmium and anelement of the sulphur group, except oxygen, such so as cadmium sulphideor cadmium selenide crystals, with a non-conductive filler and a binderare pressed into a hard mass and heated sufficiently in an oxidizingatmosphere, the surface is converted from a relatively non-conductivema-=- terial into a good electrical conductor because of the conversionof cadmium sulphide or cadmium selenide into cadmium oxide over thesurface of the element. Cadmium telluride also may be so oxidized, butits use is not as satisfactory. By

varying the time of heating, and the concentration of the oxidizingatmosphere, resistances of various ranges are obtainable. Cadmium oxideis a good electrical conductor having the desirable characteristic of anegligible temperature resistance coeflicient. This is quite differentfrom other.

electronically conductive crystals which have a high negativetemperature resistance co-efiicient.

The preferred method for making this resistance element is to mixcadmium sulphide or .40 selenide with a suitable binder, such as 2%sodium silicate or lead borate, compress the mixture under high pressureinto the desired form and heat the mass until it is completely sinteredin a non-oxidizing atmosphere such as nitrogen.

For a variable resistance having an exponential relation of resistancesalong its length, various portions of the surface of the cadmiumsulphide or cadmium selenide elements are exposed to an oxidizing heatwhich converts the con- 5 tacting portion into cadmium oxide, the timeof exposure, the temperature and the concentration of oxygen determiningthe ultimate electrical resistance value for each area so treated, theresistance decreasingv with the temperature, the concentration and timeof application. Terminals with a suitable movable contact member areprovided.

For a uniform resistance value along the length, the compressed andsintered cadmium compound element is placed in an oxidizing furnace andby continuous measurement, its resistance value can be fixed at anypoint, when the element. is removed from further exposure. Likewise adefinite resistance may be fixed over any section. For high resistancesI have found that by the addition of a filler of zircite, a hard masshaving much higher resistance values is yielded.

Reference is made to the accompanying drawing in which Fig. 1 representsa plan' view of a rheostat and Fig. 2 a section view thereof embodyingthe invention.

Referring more particularly to the drawing, at 1 is a compressed andsintered arcuate resistance plate composed of cadmium sulphide crystalswith a binder and having a surface layer of varying thicknesses ofcadmium oxide. The plate rests upon an insulating base 2, attachedthereto by terminals 3 and 4. A rotatable conductive arm 5, having acontact electrode 6, is mounted upon shaft 7 and connected in a circuitby conduc- 80 tive plate 8 on shaft 7. At 9 is'a knob for rotating arm 5and nut 10, 11 being a compression spring to insure uniform pressurebetween the resistance element and contact electrode 6.

What I claim is:

1. A resistancev element having a base com posed of a compound ofcadmium with one of the elements sulphur, selenium and telluriurn, andhaving a surface layer composed of cadmium oxide reduced in situ fromthe said base compound.

2. A resistance element as in claim 1 in which different sectors of theresistance element surface have different resistance values.

3. A resistance element as in claim 1 in which the cadmium oxide variesin depth along the length thereof.

4.. A resistance element having a base composed of cadmium sulphide andhaving a surface layer composed of cadmium oxide reduced in 100 situfrom said cadmium sulphide base.

5. A resistance element having a base composed of cadmium selenide andhaving a surface layer composed of cadmium oxide reduced in situ fromsaid cadmium selenide base.

6. A resistance element having a base composed of cadmium telluride andhaving a surface layer composed of cadmium oxide reduced in situ fromsaid cadmium telluride base.

7. A variable resistance device comprising a 110 and a contact memberadapted to make selective electrical connection with said cadmium 0xidesurface along its length.

9. The method of making a resistance element which consists in heating abase compound composed of cadmium and one of the elements sulphur,selenium and tellurium, in an oxidizing atmosphere until said basecompound surface is reduced to cadmium oxide.

SAMUEL RUBEN.

